Foils are coated with photo resist and the resist then dried or cured. After the resist coating is dried, the resist is then exposed to a patterned image of ultraviolet radiation to activate the resist material in selected regions and then the exposed portion of the photo resist foil coating is removed by washing prior to further processing steps.
The foils that are coated and cured may be used for the making of masks that are then used to define the electrical conductor patterns on the ceramic substrates known as green sheets or for electronic circuit chip manufacture. The masks may be used in a screening process where a metalized paste is screened through the mask openings and deposited on the green sheet. Alternatively, the conductor patterns may be made by metal vaporization and the metal vapor then depositing and condensing on the green sheet to form the conductor pattern.
The resist material is a commercially available photo resist such as MICROPOSIT 111 available from Shipley Company, Inc. of Newton, Mass. or other photo resist materials available from other suppliers. The example photo resist is a resinous material dissolved in a volatile solvent. The components of the resist solution are 2-ethoxy ethyl acetate, n-butyl acetate, xylene, toluene, Novalac resins and photoactive compounds. The solvent must be removed from the coating prior to imaging and such drying of the coating is known as curing. Due to the extremely fine patterns which are exposed on the resist coatings, the application of the resist and the drying of the resist layer is performed in a clean room environment, using an automated manipulating device or robot. The size of the operating envelope of the robot is limited and accordingly, the resist dryer must be of a relatively small size so that it may be placed in proximity to the robot.
The dryer must also be capable of drying the resist layer in a relatively short time in order that the flow of work progresses in a timely fashion.
Further the resist should be dried such that a uniform drying rate is maintained in order to insure a uniform thickness and quality in the resist layer. The resist layer is very thin, on the order of 25,000 Angstroms. Very slight variations in the thickness will greatly affect the end result after the film is exposed by ultraviolet radiation and the exposed portions removed.
One of the variables in the drying of the resist film is the temperature at which the drying occurs. In order to achieve uniform drying, a uniform temperature in the curing enclosure or chamber is necessary. The control of the heating elements of the dryer is essential and critical to the operation of the device and the efficient and effective curing of the photo resist coating. Typically the larger the oven or drying device, the more uniform the heating of the object, since hot spots and cold regions tend to even out when displaced from the object being heated. In larger ovens the distances may be increased, while the temperature variations are more emphasized in more compact ovens or heater devices. However, in environments where there is limited space, the heating elements must be confined in a smaller device and thus may not be significantly displaced from the item being heated, to insure uniformity of temperature. In a compact dryer unit, it is necessary to resort to other techniques of insuring temperature uniformity.
As resist coatings are dried or cured, the solvent of the resist solution is vaporized or driven off into the atmosphere. If the solvent concentration is built up in the dryer, the evaporation and removal of solvent from the resist layer is inhibited. Accordingly, the concentration of solvent in the atmosphere of the work place is an important factor in the proper curing of the resist layers on the foils.
Heaters and ovens using resistance heaters are well known in the art and examples of such ovens are U.S. Pat. No. 3,074,342 to Wachtel and 4,238,669 to Huntley. The Huntley patent additionally uses a heating lamp such as a quartz bulb to supplement the resistance heaters. Both of the ovens of Wachtel and Huntley are designed to warm or cook food items, where the emissions are not important and the uniformity of the heating is not critical, and no special precautions are taken to effect uniform heating.
U.S. Pat. No. 4,554,437 to Wagner et al. discloses a tunnel oven for the continuous through put of items to be heated. The heating of the oven is accomplished by radiant heaters heating a slab of metal such as steel which is thick enough to create a thermal mass within the oven and emit infra-red radiation to heat the food being passed through the tunnel oven. Heating in an open ended tunnel oven will not be uniform and there is no need to control emissions in the oven atmosphere when cooking food is concerned.
U.S. Pat. No. 3,052,040 to Falanga et al. discloses an air circulation apparatus that uses heated air to heat the devices treated and to remove undesirable gases released by the heat treating process.
None of the above patents address the need for a closely controlled uniform temperature within the oven to critically control the result, heat treating of objects or cooking of food items.
It is an object of the invention to uniformly heat and cure photo resist coatings on foils.
It is another object of the invention to remove the solvent concentrations in the dryer atmosphere to enhance drying uniformity, and to remove the solvent to a point of dispersal or recovery.
It is a still further object of the invention to accomplish the uniformity in heating and drying in a small device.